Association of free-living diet composition with plasma lipoprotein(a) levels in healthy adults.

BACKGROUND: Lipoprotein (a) [Lp(a)] is an apoB100-containing lipoprotein with high levels being positively associated with atherosclerotic cardiovascular disease. Lp(a) levels are genetically determined. However, previous studies report a negative association between Lp(a) and saturated fatty acid intake. Currently, apoB100 lowering therapies are used to lower Lp(a) levels, and apheresis therapy is FDA approved for patients with extreme elevations of Lp(a). The current study analyzed the association of free-living diet components with plasma Lp(a) levels. METHODS: Dietary composition data was collected during screening visits for enrollment in previously completed lipid and lipoprotein metabolism studies at Columbia University Irving Medical Center via a standardized protocol by registered dietitians using 24 hour recalls. Data were analyzed with the Nutrition Data System for Research (Version 2018). Diet quality was calculated using the Healthy Eating Index (HEI) score. Fasting plasma Lp(a) levels were measured via an isoform-independent ELISA and apo(a) isoforms were measured using gel electrophoresis. RESULTS: We enrolled 28 subjects [Black (n = 18); Hispanic (n = 7); White (n = 3)]. The mean age was 48.3 ± 12.5 years with 17 males. Median level of Lp(a) was 79.9 nmol/L (34.4-146.0) and it was negatively associated with absolute (grams/day) and relative (percent of total calories) intake of dietary saturated fatty acids (SFA) (R = -0.43, P = 0.02, SFA …(% CAL): R = -0.38, P = 0.04), palmitic acid intake (R = -0.38, P = 0.05), and stearic acid intake (R = -0.40, P = 0.03). Analyses of associations with HEI score when stratified based on Lp(a) levels > or ≤ 100 nmol/L revealed no significant associations with any of the constituent factors. CONCLUSIONS: Using 24 hour recall, we confirm previous findings that Lp(a) levels are negatively associated with dietary saturated fatty acid intake. Additionally, Lp(a) levels are not related to diet quality, as assessed by the HEI score. The mechanisms underlying the relationship of SFA with Lp(a) require further investigation.

TM6SF2 Determines Both the Degree of Lipidation and the Number of VLDL Particles Secreted by the Liver.

In 2014, exome-wide studies identified a glutamine176lysine (p.E167K) substitution in a protein of unknown function named transmembrane 6 superfamily member 2 (TM6SF2). The p.E167K variant was associated with increased hepatic fat content and reduced levels of plasma TG and LDL cholesterol. Over the next several years, additional studies defined the role of TM6SF2, which resides in the ER and the ER-Golgi interface, in the lipidation of nascent VLDL to generate mature, more TG-rich VLDL. Consistent results from cells and rodents indicated that the secretion of TG was reduced in the p.E167K variant or when hepatic TM6SF2 was deleted. However, data for secretion of APOB was inconsistent, either reduced or increased secretion was observed. A recent study of people homozygous for the variant demonstrated reduced in vivo secretion of large, TG-rich VLDL1 into plasma; both TG and APOB secretion were reduced. Here we present new results demonstrating increased secretion of VLDL APOB with no change in TG secretion in p.E167K homozygous individuals from the Lancaster Amish community compared to their wild-type siblings. Our in vivo kinetic tracer results are supported by in vitro experiments in HepG2 and McA cells with knock-down or Crispr-deletions of TM6SF2, respectively. We offer a model to potentially explain all of the prior data and our new results.

Relationship of apolipoprotein(a) isoform size with clearance and production of lipoprotein(a) in a diverse cohort.

Lipoprotein(a) [Lp(a)] has two main proteins, apoB100 and apo(a). High levels of Lp(a) confer an increased risk for atherosclerotic cardiovascular disease. Most people have two circulating isoforms of apo(a) differing in their molecular mass, determined by the number of Kringle IV Type 2 repeats. Previous studies report a strong inverse relationship between Lp(a) levels and apo(a) isoform sizes. The roles of Lp(a) production and fractional clearance and how ancestry affects this relationship remain incompletely defined. We therefore examined the relationships of apo(a) size with Lp(a) levels and both apo(a) fractional clearance rates (FCR) and production rates (PR) in 32 individuals not on lipid-lowering treatment. We determined plasma Lp(a) levels and apo(a) isoform sizes, and used the relative expression of the two isoforms to calculate a "weighted isoform size" (wIS). Stable isotope studies were performed, using D3-leucine, to determine the apo(a) FCR and PR. As expected, plasma Lp(a) concentrations were inversely correlated with wIS (R2 = 0.27; P = 0.002). The wIS had a modest positive correlation with apo(a) FCR (R2 = 0.10, P = 0.08), and a negative correlation with apo(a) PR (R2 = 0.11; P = 0.06). The relationship between wIS and PR became significant when we controlled for self-reported race and ethnicity (SRRE) (R2 = 0.24, P = 0.03); controlling for SRRE did not affect the relationship between wIS and FCR. Apo(a) wIS plays a role in both FCR and PR; however, adjusting for SRRE strengthens the correlation between wIS and PR, suggesting an effect of ancestry.

Medical weight management protects against weight gain during the COVID-19 pandemic.

Background: American adults have gained weight during the COVID-19 pandemic. Little is known about how patients who are medically managed for overweight and obesity, including patients who are prescribed antiobesity pharmacotherapy, have fared. Objective: To assess the COVID-19 pandemic's effect on weight, food choices, and health behaviors in patients receiving medical treatment for overweight or obesity. Methods: Adult patients treated at an urban academic weight management center between 1 May 2019 and 1 May 2020 were electronically surveyed between 23 February and 23 March 2021. The survey assessed changes in weight, eating, behaviors, and the use of antiobesity medications (AOMs) following issuance of social distancing/stay-at-home policies in March 2020. Results: In 970 respondents, median percent weight change for those taking AOMs was -0.459% [interquartile range -5.46%-(+3.73%)] compared to +2.33% [IQR -1.92%-(+6.52%)] for those not taking AOMs (p < 0.001). More participants achieved ≥5% weight loss if they were taking AOMs compared to those who were not (26.7% vs. 15.8%, p = 0.004), and weight gain ≥5% was also lower in those taking AOMs (19.8% vs. 30.3%, p = 0.004). Patients with pre-pandemic BMI ≥30 kg/m2 taking AOMs experienced the greatest weight reduction, and there was greater weight loss associated with increased physical activity. Conclusions and Relevance: Medical weight management protected against weight gain during this period of the COVID-19 pandemic. Increased physical activity, decreased alcohol intake, and use of AOMs were factors that contributed to this protective effect.

Personalized Reminders for Immunization Using Short Messaging Systems to Improve Human Papillomavirus Vaccination Series Completion: Parallel-Group Randomized Trial.

BACKGROUND: Completion rates among adolescents who initiate the human papillomavirus (HPV) vaccine 3-dose series are low. SMS text message vaccine reminders are effective, but less is known about the best types for HPV series completion or the ability to assess and target vaccine decision-making stage. OBJECTIVE: The aim of this study is to compare the effectiveness of HPV vaccine series completion in minority adolescents who received precision and educational versus conventional SMS text message reminders. METHODS: Enrolled parents of adolescents aged 9-17 years who received the first HPV vaccine dose at 1 of the 4 academic-affiliated community health clinics in New York City were randomized 1:1 to 1 of the 2 parallel, unblinded arms: precision SMS text messages (which included stage-targeted educational information, next dose due date, and site-specific walk-in hours) or conventional SMS text messages without educational information. Randomization was stratified according to gender, age, and language. The primary outcome was series completion within 12 months. In post hoc analysis, enrollees were compared with concurrent nonenrollees and historical controls. RESULTS: Overall, 956 parents were enrolled in the study. The precision (475 families) and conventional (481 families) SMS text message arms had similarly high series completion rates (344/475, 72.4% vs 364/481, 75.7%). A total of 42 days after the first dose, two-thirds of families, not initially in the preparation stage, moved to preparation or vaccinated stage. Those in either SMS text message arm had significantly higher completion rates than nonenrollees (708/1503, 47.1% vs 679/1503, 45.17%; P<.001). Even after removing those needing only 2 HPV doses, adolescents receiving any SMS text messages had higher completion rates than historical controls (337/2823, 11.93% vs 981/2823, 34.75%; P<.001). A population-wide effect was seen from 2014 to 2016, above historical trends. CONCLUSIONS: SMS text message reminders led to timely HPV vaccine series completion in a low-income, urban, minority study population and also led to population-wide effects. Educational information did not provide an added benefit to this population. TRIAL REGISTRATION: ClinicalTrials.gov NCT02236273; https://clinicaltrials.gov/ct2/show/NCT02236273.

Effect of Electronic Health Record Reminders for Routine Immunizations and Immunizations Needed for Chronic Medical Conditions.

BACKGROUND: Immunization reminders in electronic health records (EHR) provide clinical decision support (CDS) that can reduce missed immunization opportunities. Little is known about using CDS rules from a regional immunization information system (IIS) to power local EHR immunization reminders. OBJECTIVE: This study aimed to assess the impact of EHR reminders using regional IIS CDS-provided rules on receipt of immunizations in a low-income, urban population for both routine immunizations and those recommended for patients with chronic medical conditions (CMCs). METHODS: We built an EHR-based immunization reminder using the open-source resource used by the New York City IIS in which we overlaid logic regarding immunizations needed for CMCs. Using a randomized cluster-cross-over pragmatic clinical trial in four academic-affiliated clinics, we compared captured immunization opportunities during patient visits when the reminder was "on" versus "off" for the primary immunization series, school-age boosters, and adolescents. We also assessed coverage of CMC-specific immunizations. Up-to-date immunization was measured by end of quarter. Rates were compared using chi square tests. RESULTS: Overall, 15,343 unique patients were seen for 26,647 visits. The alert significantly impacted captured opportunities to complete the primary series in both well-child and acute care visits (57.6% on vs. 54.3% off, p = 0.001, and 15.3% on vs. 10.1% off, p = 0.02, respectively), among most age groups, and several immunization types. Captured opportunities for CMC-specific immunizations remained low regardless of alert status. The alert did not have an effect on up-to-date immunization overall (89.1 vs. 88.3%). CONCLUSION: CDS in this population improved captured immunization opportunities. Baseline high rates may have blunted an up-to-date population effect. Converting Centers for Disease Control and Prevention (CDC) rules to generate sufficiently sensitive and specific alerts for CMC-specific immunizations proved challenging, and the alert did not have an impact on CMC-specific immunizations, potentially highlighting need for more work in this area.

Weight-loss response to naltrexone/bupropion is modulated by the Taq1A genetic variant near DRD2 (rs1800497): A pilot study.

Naltrexone/bupropion (NB) is a US Food and Drug Administration-approved antiobesity medication. Clinical trials have shown variable weight loss, with responders and non-responders. NB is believed to act on central dopaminergic pathways to suppress appetite. The Taq1A polymorphism near DRD2 (rs1800497) is associated with the density of striatal dopamine D2 receptors, with individuals carrying the A allele (AA or AG; termed A1+) having 30%-40% fewer dopamine binding sites than those who do not carry the A allele (GG; termed A1-). We performed a pilot study to assess the association of the rs1800497 ANKK1 c.2137G > A (p.Glu713Lys) variant with weight loss with NB treatment in 33 subjects. Mean (SD) weight loss was 5.9% (3.2%) for the A1+ genotype group (n = 15) and 4.2% (4.2%) for the A1- genotype group (n = 18). The mean weight loss for the A1+ genotype group was significantly greater than the predefined clinically significant 4% weight-loss target (one-sample t-test, P = .035), whereas the mean weight loss for the A1- genotype group was not (P = .85). Individuals with the A1+ genotype appear to respond better to NB than A1- individuals.

Acute injection of a DHA triglyceride emulsion after hypoxic-ischemic brain injury in mice increases both DHA and EPA levels in blood and brain✰.

We recently reported that acute injection of docosahexaenoic acid (DHA) triglyceride emulsions (tri-DHA) conferred neuroprotection after hypoxic-ischemic (HI) injury in a neonatal mouse stroke model. We showed that exogenous DHA increased concentrations of DHA in brain mitochondria as well as DHA-derived specialized pro-resolving mediator (SPM) levels in the brain. The objective of the present study was to investigate the distribution of emulsion particles and changes in plasma lipid profiles after tri-DHA injection in naïve mice and in animals subjected to HI injury. We also examined whether tri-DHA injection would change DHA- and eicosapentaenoic acid (EPA)-derived SPM levels in the brain. To address this, neonatal (10-day-old) naïve and HI mice were injected with radiolabeled tri-DHA emulsion (0.375 g tri-DHA/kg bw), and blood clearance and tissue distribution were analyzed. Among all the organs assayed, the lowest uptake of emulsion particles was in the brain (<0.4% recovered dose) in both naïve and HI mice, while the liver had the highest uptake. Tri-DHA administration increased DHA concentrations in plasma lysophosphatidylcholine and non-esterified fatty acids. Additionally, treatment with tri-DHA after HI injury significantly elevated the levels of DHA-derived SPMs and monohydroxy-containing DHA-derived products in the brain. Further, tri-DHA administration increased resolvin E2 (RvE2, 5S,18R-dihydroxy-eicosa-6E,8Z,11Z,14Z,16E-pentaenoic acid) and monohydroxy-containing EPA-derived products in the brain. These results suggest that the transfer of DHA through plasma lipid pools plays an important role in DHA brain transport in neonatal mice subjected to HI injury. Furthermore, increases in EPA and EPA-derived SPMs following tri-DHA injection demonstrate interlinked metabolism of these two fatty acids. Hence, changes in both EPA and DHA profile patterns need to be considered when studying the protective effects of DHA after HI brain injury. Our results highlight the need for further investigation to differentiate the effects of DHA from EPA on neuroprotective pathways following HI damage. Such information could contribute to the development of specific DHA-EPA formulations to improve clinical endpoints and modulate potential biomarkers in ischemic brain injury.

The Type and Amount of Dietary Fat Affect Plasma Factor VIIc, Fibrinogen, and PAI-1 in Healthy Individuals and Individuals at High Cardiovascular Disease Risk: 2 Randomized Controlled Trials.

BACKGROUND: Factor VIIc, fibrinogen, and plasminogen activator inhibitor 1 (PAI-1) are cardiovascular disease (CVD) risk factors and are modulated, in part, by fat type and amount. OBJECTIVE: We evaluated fat type and amount on the primary outcomes: factor VIIc, fibrinogen, and PAI-1. METHODS: In the Dietary Effects on Lipoproteins and Thrombogenic Activity (DELTA) Trial, 2 controlled crossover feeding studies evaluated substituting carbohydrate or MUFAs for SFAs. Study 1: healthy participants (n = 103) were provided with (8 wk) an average American diet [AAD; designed to provide 37% of energy (%E) as fat, 16% SFA], a Step 1 diet (30%E fat, 9% SFA), and a diet low in SFA (Low-Sat; 26%E fat, 5% SFA). Study 2: participants (n = 85) at risk for CVD and metabolic syndrome (MetSyn) were provided with (7 wk) an AAD, a step 1 diet, and a high-MUFA diet (designed to provide 37%E fat, 8% SFA, 22% MUFA). RESULTS: Study 1: compared with AAD, the Step 1 and Low-Sat diets decreased mean factor VIIc by 1.8% and 2.6% (overall P = 0.0001), increased mean fibrinogen by 1.2% and 2.8% (P = 0.0141), and increased mean square root PAI-1 by 0.0% and 6.0% (P = 0.0037), respectively. Study 2: compared with AAD, the Step 1 and high-MUFA diets decreased mean factor VIIc by 4.1% and 3.2% (overall P < 0.0001), increased mean fibrinogen by 3.9% and 1.5% (P = 0.0083), and increased mean square-root PAI-1 by 2.0% and 5.8% (P = 0.1319), respectively. CONCLUSIONS: Replacing SFA with carbohydrate decreased factor VIIc and increased fibrinogen in healthy and metabolically unhealthy individuals and also increased PAI-1 in healthy subjects. Replacing SFA with MUFA decreased factor VIIc and increased fibrinogen but less than carbohydrate. Our results indicate an uncertain effect of replacing SFA with carbohydrate or MUFA on cardiometabolic risk because of small changes in hemostatic factors and directionally different responses to decreasing SFA. This trial was registered at https://clinicaltrials.gov/ct2/show/NCT00000538?term=NCT00000538&rank=1 as NCT00000538.

Cholesterol Stabilizes TAZ in Hepatocytes to Promote Experimental Non-alcoholic Steatohepatitis.

Incomplete understanding of how hepatosteatosis transitions to fibrotic non-alcoholic steatohepatitis (NASH) has limited therapeutic options. Two molecules that are elevated in hepatocytes in human NASH liver are cholesterol, whose mechanistic link to NASH remains incompletely understood, and TAZ, a transcriptional regulator that promotes fibrosis but whose mechanism of increase in NASH is unknown. We now show that increased hepatocyte cholesterol upregulates TAZ and promotes fibrotic NASH. ASTER-B/C-mediated internalization of plasma membrane cholesterol activates soluble adenylyl cyclase (sAC; ADCY10), triggering a calcium-RhoA-mediated pathway that suppresses ß-TrCP/proteasome-mediated TAZ degradation. In mice fed with a cholesterol-rich NASH-inducing diet, hepatocyte-specific silencing of ASTER-B/C, sAC, or RhoA decreased TAZ and ameliorated fibrotic NASH. The cholesterol-TAZ pathway is present in primary human hepatocytes, and associations among liver cholesterol, TAZ, and RhoA in human NASH liver are consistent with the pathway. Thus, hepatocyte cholesterol contributes to fibrotic NASH by increasing TAZ, suggesting new targets for therapeutic intervention.

Vitamin E absorption and kinetics in healthy women, as modulated by food and by fat, studied using 2 deuterium-labeled α-tocopherols in a 3-phase crossover design.

BACKGROUND: Determining the human vitamin E [α-tocopherol (α-T)] requirement is difficult, and novel approaches to assess α-T absorption and trafficking are needed. OBJECTIVE: We hypothesized that the dual-isotope technique, using 2 deuterium-labeled [intravenous (IV) d6- and oral d3-] α-T, would be effective in determining α-T fractional absorption. Further, defined liquid meal (DLM) fat or fasting would modulate α-T fractional absorption and lipoprotein transport. METHODS: A 3-phase cr ossover design was used. At 0 h, participants received IV d6-α-T and consumed d3-α-T with a 600-kcal DLM (40% or 0% fat) followed by controlled meals or by the 0% fat DLM, a 12-h fast, and then controlled meals. Blood samples and fecal samples were collected at intervals and analyzed by LC-MS. Pharmacokinetic parameters were calculated from plasma tracer concentrations and enrichments. Fractional absorption was calculated from d3- to d6-α-T areas under the curve, from a novel mathematical model, and from the balance method (oral d3-α-T minus fecal d3-α-T excreted). RESULTS: Estimated α-T fractional absorption during the 40% fat intervention was 55% ± 3% (mean ± SEM; n = 10), which was 9% less than during the 0% fat intervention (64% ± 3%, n = 10; P < 0.02). Fasting had no apparent effect (56% ± 3%, n = 7), except it slowed plasma oral d3-α-T appearance. Both balance data and model outcomes confirmed that the DLM fat did not potentiate d3-α-T absorption. During the IV emulsion clearance, HDL rapidly acquired d6-α-T (21 ± 2 nmol/L plasma per minute). During the first 8 h postdosing, triglyceride-rich lipoproteins (TRLs) were preferentially d3-α-T enriched relative to LDL or HDL, showing the TRL precursor role. CONCLUSIONS: Quantitatively, α-T absorption is not limited by fat absence or by fasting. However, α-T leaves the intestine by a process that is prolonged during fasting and potentiated by eating, suggesting that α-T absorption is highly dependent on chylomicron assembly processes. This trial was registered at clinicaltrials.gov as NCT00862433.

An ATF6-tPA pathway in hepatocytes contributes to systemic fibrinolysis and is repressed by DACH1.

Tissue-type plasminogen activator (tPA) is a major mediator of fibrinolysis and, thereby, prevents excessive coagulation without compromising hemostasis. Studies on tPA regulation have focused on its acute local release by vascular cells in response to injury or other stimuli. However, very little is known about sources, regulation, and fibrinolytic function of noninjury-induced systemic plasma tPA. We explore the role and regulation of hepatocyte-derived tPA as a source of basal plasma tPA activity and as a contributor to fibrinolysis after vascular injury. We show that hepatocyte tPA is downregulated by a pathway in which the corepressor DACH1 represses ATF6, which is an inducer of the tPA gene Plat Hepatocyte-DACH1-knockout mice show increases in liver Plat, circulating tPA, fibrinolytic activity, bleeding time, and time to thrombosis, which are reversed by silencing hepatocyte Plat Conversely, hepatocyte-ATF6-knockout mice show decreases in these parameters. The inverse correlation between DACH1 and ATF6/PLAT is conserved in human liver. These findings reveal a regulated pathway in hepatocytes that contributes to basal circulating levels of tPA and to fibrinolysis after vascular injury.

Effects of APOC3 Heterozygous Deficiency on Plasma Lipid and Lipoprotein Metabolism.

Objective- Apo (apolipoprotein) CIII inhibits lipoprotein lipase (LpL)-mediated lipolysis of VLDL (very-low-density lipoprotein) triglyceride (TG) and decreases hepatic uptake of VLDL remnants. The discovery that 5% of Lancaster Old Order Amish are heterozygous for the APOC3 R19X null mutation provided the opportunity to determine the effects of a naturally occurring reduction in apo CIII levels on the metabolism of atherogenic containing lipoproteins. Approach and Results- We conducted stable isotope studies of VLDL-TG and apoB100 in 5 individuals heterozygous for the null mutation APOC3 R19X (CT) and their unaffected (CC) siblings. Fractional clearance rates and production rates of VLDL-TG and apoB100 in VLDL, IDL (intermediate-density lipoprotein), LDL, apo CIII, and apo CII were determined. Affected (CT) individuals had 49% reduction in plasma apo CIII levels compared with CCs ( P<0.01) and reduced plasma levels of TG (35%, P<0.02), VLDL-TG (45%, P<0.02), and VLDL-apoB100 (36%, P<0.05). These changes were because of higher fractional clearance rates of VLDL-TG and VLDL-apoB100 with no differences in production rates. CTs had higher rates of the conversion of VLDL remnants to LDL compared with CCs. In contrast, rates of direct removal of VLDL remnants did not differ between the groups. As a result, the flux of apoB100 from VLDL to LDL was not reduced, and the plasma levels of LDL-cholesterol and LDL-apoB100 were not lower in the CT group. Apo CIII production rate was lower in CTs compared with CCs, whereas apo CII production rate was not different between the 2 groups. The fractional clearance rates of both apo CIII and apo CII were higher in CTs than CCs. Conclusions- These studies demonstrate that 50% reductions in plasma apo CIII, in otherwise healthy subjects, results in a significantly higher rate of conversion of VLDL to LDL, with little effect on direct hepatic uptake of VLDL. When put in the context of studies demonstrating significant protection from cardiovascular events in individuals with loss of function variants in the APOC3 gene, our results provide strong evidence that therapies which increase the efficiency of conversion of VLDL to LDL, thereby reducing remnant concentrations, should reduce the risk of cardiovascular disease.

Effects of mipomersen, an apolipoprotein B100 antisense, on lipoprotein (a) metabolism in healthy subjects.

Elevated lipoprotein (a) [Lp(a)] levels increase the risk for CVD. Novel treatments that decrease LDL cholesterol (LDL-C) have also shown promise for reducing Lp(a) levels. Mipomersen, an antisense oligonucleotide that inhibits apoB synthesis, is approved for the treatment of homozygous familial hypercholesterolemia. It decreases plasma levels of LDL-C by 25% to 39% and lowers levels of Lp(a) by 21% to 39%. We examined the mechanisms for Lp(a) lowering during mipomersen treatment. We enrolled 14 healthy volunteers who received weekly placebo injections for 3 weeks followed by weekly injections of mipomersen for 7 weeks. Stable isotope kinetic studies were performed using deuterated leucine at the end of the placebo and mipomersen treatment periods. The fractional catabolic rate (FCR) of Lp(a) was determined from the enrichment of a leucine-containing peptide specific to apo(a) by LC/MS. The production rate (PR) of Lp(a) was calculated from the product of Lp(a) FCR and Lp(a) concentration (converted to pool size). In a diverse population, mipomersen reduced plasma Lp(a) levels by 21%. In the overall study group, mipomersen treatment resulted in a 27% increase in the FCR of Lp(a) with no significant change in PR. However, there was heterogeneity in the response to mipomersen therapy, and changes in both FCRs and PRs affected the degree of change in Lp(a) concentrations. Mipomersen treatment decreases Lp(a) plasma levels mainly by increasing the FCR of Lp(a), although changes in Lp(a) PR were significant predictors of reductions in Lp(a) levels in some subjects.

MerTK signaling in macrophages promotes the synthesis of inflammation resolution mediators by suppressing CaMKII activity.

Inflammation resolution counterbalances excessive inflammation and restores tissue homeostasis after injury. Failure of resolution contributes to the pathology of numerous chronic inflammatory diseases. Resolution is mediated by endogenous specialized proresolving mediators (SPMs), which are derived from long-chain fatty acids by lipoxygenase (LOX) enzymes. 5-LOX plays a critical role in the biosynthesis of two classes of SPMs: lipoxins and resolvins. Cytoplasmic localization of the nonphosphorylated form of 5-LOX is essential for SPM biosynthesis, whereas nuclear localization of phosphorylated 5-LOX promotes proinflammatory leukotriene production. We previously showed that MerTK, an efferocytosis receptor on macrophages, promotes SPM biosynthesis by increasing the abundance of nonphosphorylated, cytoplasmic 5-LOX. We now show that activation of MerTK in human macrophages led to ERK-mediated expression of the gene encoding sarcoplasmic/endoplasmic reticulum calcium ATPase 2 (SERCA2), which decreased the cytosolic Ca2+ concentration and suppressed the activity of calcium/calmodulin-dependent protein kinase II (CaMKII). This, in turn, reduced the activities of the mitogen-activated protein kinase (MAPK) p38 and the kinase MK2, resulting in the increased abundance of the nonphosphorylated, cytoplasmic form of 5-LOX and enhanced SPM biosynthesis. In a zymosan-induced peritonitis model, an inflammatory setting in which macrophage MerTK activation promotes resolution, inhibition of ERK activation delayed resolution, which was characterized by an increased number of neutrophils and decreased amounts of SPMs in tissue exudates. These findings contribute to our understanding of how MerTK signaling induces 5-LOX-derived SPM biosynthesis and suggest a therapeutic strategy to boost inflammation resolution in settings where defective resolution promotes disease progression.

Metformin and AMP Kinase Activation Increase Expression of the Sterol Transporters ABCG5/8 (ATP-Binding Cassette Transporter G5/G8) With Potential Antiatherogenic Consequences.

OBJECTIVE: The mechanisms underlying the cardiovascular benefit of the anti-diabetic drug metformin are poorly understood. Recent studies have suggested metformin may upregulate macrophage reverse cholesterol transport. The final steps of reverse cholesterol transport are mediated by the sterol transporters, ABCG5 (ATP-binding cassette transporter G5) and ABCG8 (ATP-binding cassette transporter G8), which facilitate hepato-biliary transport of cholesterol. This study was undertaken to assess the possibility that metformin induces Abcg5 and Abcg8 expression in liver and to elucidate the underlying mechanisms. APPROACH AND RESULTS: Metformin-treated mouse or human primary hepatocytes showed increased expression of Abcg5/8 and the bile salt export pump, Bsep. Administration of metformin to Western-type diet-fed mice showed significant upregulation of Abcg5/8 and Bsep. This resulted in increased initial clearance of 3H-cholesteryl ester HDL (high-density lipoprotein) from plasma. However, fecal 3H-cholesterol output was only marginally increased, possibly reflecting increased hepatic Ldlr (low-density lipoprotein receptor) expression, which would increase nonradiolabeled cholesterol uptake. Abcg5/8 undergo strong circadian variation. Available chromatin immunoprecipitation-Seq data suggested multiple binding sites for Period 2, a transcriptional repressor, within the Abcg5/8 locus. Addition of AMPK (5' adenosine monophosphate-activated protein kinase) agonists decreased Period 2 occupancy, suggesting derepression of Abcg5/8. Inhibition of ATP citrate lyase, which generates acetyl-CoA from citrate, also decreased Period 2 occupancy, with concomitant upregulation of Abcg5/8. This suggests a mechanistic link between feeding-induced acetyl-CoA production and decreased cholesterol excretion via Period 2, resulting in inhibition of Abcg5/8 expression. CONCLUSIONS: Our findings provide partial support for the concept that metformin may provide cardiovascular benefit via increased reverse cholesterol transport but also indicate increased Ldlr expression as a potential additional mechanism. AMPK activation or ATP citrate lyase inhibition may mediate antiatherogenic effects through increased ABCG5/8 expression.

FoxO transcription factors are required for hepatic HDL cholesterol clearance.

Insulin resistance and type 2 diabetes are associated with low levels of high-density lipoprotein cholesterol (HDL-C). The insulin-repressible FoxO transcription factors are potential mediators of the effect of insulin on HDL-C. FoxOs mediate a substantial portion of insulin-regulated transcription, and poor FoxO repression is thought to contribute to the excessive glucose production in diabetes. In this work, we show that mice with liver-specific triple FoxO knockout (L-FoxO1,3,4), which are known to have reduced hepatic glucose production, also have increased HDL-C. This was associated with decreased expression of the HDL-C clearance factors scavenger receptor class B type I (SR-BI) and hepatic lipase and defective selective uptake of HDL cholesteryl ester by the liver. The phenotype could be rescued by re-expression of SR-BI. These findings demonstrate that hepatic FoxOs are required for cholesterol homeostasis and HDL-mediated reverse cholesterol transport to the liver.

CETP (Cholesteryl Ester Transfer Protein) Inhibition With Anacetrapib Decreases Production of Lipoprotein(a) in Mildly Hypercholesterolemic Subjects.

OBJECTIVE: Lp(a) [lipoprotein (a)] is composed of apoB (apolipoprotein B) and apo(a) [apolipoprotein (a)] and is an independent risk factor for cardiovascular disease and aortic stenosis. In clinical trials, anacetrapib, a CETP (cholesteryl ester transfer protein) inhibitor, causes significant reductions in plasma Lp(a) levels. We conducted an exploratory study to examine the mechanism for Lp(a) lowering by anacetrapib. APPROACH AND RESULTS: We enrolled 39 participants in a fixed-sequence, double-blind study of the effects of anacetrapib on the metabolism of apoB and high-density lipoproteins. Twenty-nine patients were randomized to atorvastatin 20 mg/d, plus placebo for 4 weeks, and then atorvastatin plus anacetrapib (100 mg/d) for 8 weeks. The other 10 subjects were randomized to double placebo for 4 weeks followed by placebo plus anacetrapib for 8 weeks. We examined the mechanisms of Lp(a) lowering in a subset of 12 subjects having both Lp(a) levels >20 nmol/L and more than a 15% reduction in Lp(a) by the end of anacetrapib treatment. We performed stable isotope kinetic studies using 2H3-leucine at the end of each treatment to measure apo(a) fractional catabolic rate and production rate. Median baseline Lp(a) levels were 21.5 nmol/L (interquartile range, 9.9-108.1 nmol/L) in the complete cohort (39 subjects) and 52.9 nmol/L (interquartile range, 38.4-121.3 nmol/L) in the subset selected for kinetic studies. Anacetrapib treatment lowered Lp(a) by 34.1% (P≤0.001) and 39.6% in the complete and subset cohort, respectively. The decreases in Lp(a) levels were because of a 41% reduction in the apo(a) production rate, with no effects on apo(a) fractional catabolic rate. CONCLUSIONS: Anacetrapib reduces Lp(a) levels by decreasing its production. CLINICAL TRIAL REGISTRATION: URL: http://www.clinicaltrials.gov. Unique identifier: NCT00990808.

The metabolism of lipoprotein (a): an ever-evolving story.

Lipoprotein (a) [Lp(a)] is characterized by apolipoprotein (a) [apo(a)] covalently bound to apolipoprotein B 100. It was described in human plasma by Berg et al. in 1963 and the gene encoding apo(a) (LPA) was cloned in 1987 by Lawn and colleagues. Epidemiologic and genetic studies demonstrate that increases in Lp(a) plasma levels increase the risk of atherosclerotic cardiovascular disease. Novel Lp(a) lowering treatments highlight the need to understand the regulation of plasma levels of this atherogenic lipoprotein. Despite years of research, significant uncertainty remains about the assembly, secretion, and clearance of Lp(a). Specifically, there is ongoing controversy about where apo(a) and apoB-100 bind to form Lp(a); which apoB-100 lipoproteins bind to apo(a) to create Lp(a); whether binding of apo(a) is reversible, allowing apo(a) to bind to more than one apoB-100 lipoprotein during its lifespan in the circulation; and how Lp(a) or apo(a) leave the circulation. In this review, we highlight past and recent data from stable isotope studies of Lp(a) metabolism, highlighting the critical metabolic uncertainties that exist. We present kinetic models to describe results of published studies using stable isotopes and suggest what future studies are required to improve our understanding of Lp(a) metabolism.

Effects of CETP inhibition with anacetrapib on metabolism of VLDL-TG and plasma apolipoproteins C-II, C-III, and E.

Cholesteryl ester transfer protein (CETP) mediates the transfer of HDL cholesteryl esters for triglyceride (TG) in VLDL/LDL. CETP inhibition, with anacetrapib, increases HDL-cholesterol, reduces LDL-cholesterol, and lowers TG levels. This study describes the mechanisms responsible for TG lowering by examining the kinetics of VLDL-TG, apoC-II, apoC-III, and apoE. Mildly hypercholesterolemic subjects were randomized to either placebo (N = 10) or atorvastatin 20 mg/qd (N = 29) for 4 weeks (period 1) followed by 8 weeks of anacetrapib, 100 mg/qd (period 2). Following each period, subjects underwent stable isotope metabolic studies to determine the fractional catabolic rates (FCRs) and production rates (PRs) of VLDL-TG and plasma apoC-II, apoC-III, and apoE. Anacetrapib reduced the VLDL-TG pool on a statin background due to an increased VLDL-TG FCR (29%; P = 0.002). Despite an increased VLDL-TG FCR following anacetrapib monotherapy (41%; P = 0.11), the VLDL-TG pool was unchanged due to an increase in the VLDL-TG PR (39%; P = 0.014). apoC-II, apoC-III, and apoE pool sizes increased following anacetrapib; however, the mechanisms responsible for these changes differed by treatment group. Anacetrapib increased the VLDL-TG FCR by enhancing the lipolytic potential of VLDL, which lowered the VLDL-TG pool on atorvastatin background. There was no change in the VLDL-TG pool in subjects treated with anacetrapib monotherapy due to an accompanying increase in the VLDL-TG PR.